Gallery: Bad weather hampered the start of the demolition as very little work took place during the early morning amid the rubble from the explosion Tuesday, Dec. 5, 2017, in Minneapolis, MN. DAVID JOLES � david.joles@startribune.com Construction crews begin demolition of the Minnehaha Academy campus damaged by a natural gas explosion. ,cq

David Joles – Star Tribune

Gallery: A worker climbs off of a skid loader amid the rubble from the explosion Tuesday, Dec. 5, 2017, in Minneapolis, MN.

Demolition crews began clearing debris from Minnehaha Academy’s Upper School on Wednesday morning, four months after a deadly natural gas explosion caused significant damage to the building.

School officials expect it will take up to six weeks to clear the damaged portions of the site at 3100 West River Parkway in Minneapolis. Then, they plan to rebuild.

The two major parts of the Upper School that are still standing — housing the arts and athletics wings plus the chapel auditorium — have been reinforced because they were not designed as stand-alone buildings, school officials said.

Engineers have spent the past weeks sorting through the best way to separate the debris from those structures. The portions of the school destroyed by the blast were built in 1912 and 1922.

“They have to be separated from the healthy areas in a very strategic way so that the healthy buildings can stay up,” said Sara Jacobson, the private Christian school’s executive director of institutional advancement.

A fence adorned with flowers, ribbons curved into heart shapes and prayer cards surrounds the damaged property. The class of 2018 left a sign that reads, “You can’t shake our foundation.”

Construction crews begin demolition of the Minnehaha Academy campus damaged by a natural gas explosion. Here, workers walk by the rubble from the explosion. DAVID JOLES david.joles@startribune.com

Mark Brandt, who lives five blocks away from the school, said he misses the students’ presence in the neighborhood.

“It’s so different,” Brandt said. “Now it’s barren and quiet. You sort of miss the vitality they gave to the neighborhood.”

The Upper School and its roughly 350 students in grades nine through 12 is now in temporary class space at a former college campus in Mendota Heights.

Jacobson said they expect to move back to the original campus by fall 2019.

“The students are doing well at Mendota,” she said. “They are resilient.”

She said school officials have added extra activities to cheer the kids up. The students played pickup dodge ball in the parking lot at Mendota and they’ll go on a retreat this winter.

School officials have already sought proposals from companies interested in working on the rebuilding project. Eight developers have responded, Jacobson said, and the school expects to pick a firm by next week to do the work.

The cost of the project is still unclear, Jacobson, but the school is relying on insurance to cover a significant portion of the recovery. The school has also begun fundraising to cover any remaining expenses.

The blast killed receptionist Ruth Berg, 47, and janitor John F. Carlson, 82, and injured nine other people, one critically.